Isotopes of rubidium

Rubidium (₃₇Rb) has 32 isotopes, with naturally occurring rubidium being composed of just two isotopes; ⁸⁵Rb (72.2%) and the radioactive ⁸⁷Rb (27.8%). Normal mixes of rubidium are radioactive enough to fog photographic film in approximately 30 to 60 days.

Main isotopes of rubidium (₃₇Rb)

Iso­tope Decay abun­dance half-life (t1/2) mode pro­duct ^83Rb syn 86.2 d ε ^83Kr γ – ^84Rb syn 32.9 d ε ^84Kr β^+ ^84Kr γ – β^− ^84Sr ^85Rb 72.17% stable ^86Rb syn 18.7 d β^− ^86Sr γ – ^87Rb 27.83% 4.9×10^10 y β^− ^87Sr
Standard atomic weight Ar, standard(Rb)	85.4678(3)[1]

⁸⁷Rb has a half-life of 4.92×10¹⁰ years. It readily substitutes for potassium in minerals, and is therefore fairly widespread. ⁸⁷Rb has been used extensively in dating rocks; ⁸⁷Rb decays to stable strontium-87 by emission of a negative beta particle, i.e. an electron ejected from the nucleus. During fractional crystallization, Sr tends to become concentrated in plagioclase, leaving Rb in the liquid phase. Hence, the Rb/Sr ratio in residual magma may increase over time, resulting in rocks with increasing Rb/Sr ratios with increasing differentiation. Highest ratios (10 or higher) occur in pegmatites. If the initial amount of Sr is known or can be extrapolated, the age can be determined by measurement of the Rb and Sr concentrations and the ⁸⁷Sr/⁸⁶Sr ratio. The dates indicate the true age of the minerals only if the rocks have not been subsequently altered. See rubidium–strontium dating for a more detailed discussion.

Other than ⁸⁷Rb, the longest-lived radioisotopes are ⁸³Rb with a half-life of 86.2 days, ⁸⁴Rb with a half-life of 33.1 days, and ⁸⁶Rb with a half-life of 18.642 days. All other radioisotopes have half-lives less than a day.

⁸²Rb is used in some cardiac positron emission tomography scans to assess myocardial perfusion. It has a half-life of 1.273 minutes. It does not exist naturally, but can be made from the decay of ⁸²Sr.

List of isotopes

Nuclide [n 1]	Z	N	Isotopic mass (Da) [n 2][n 3]	Half-life [n 4][n 5]	Decay mode [n 6]	Daughter isotope [n 7][n 8]	Spin and parity [n 9][n 5]	Natural abundance (mole fraction)
	Excitation energy[n 5]							Normal proportion	Range of variation
^71Rb	37	34	70.96532(54)#		p	^70Kr	5/2−#
^72Rb	37	35	71.95908(54)#	<1.5 μs	p	^71Kr	3+#
^72mRb	100(100)# keV			1# μs	p	^71Kr	1−#
^73Rb	37	36	72.95056(16)#	<30 ns	p	^72Kr	3/2−#
^74Rb	37	37	73.944265(4)	64.76(3) ms	β^+	^74Kr	(0+)
^75Rb	37	38	74.938570(8)	19.0(12) s	β^+	^75Kr	(3/2−)
^76Rb	37	39	75.9350722(20)	36.5(6) s	β^+	^76Kr	1(−)
					β^+, α (3.8×10^−7%)	^72Se
^76mRb	316.93(8) keV			3.050(7) μs			(4+)
^77Rb	37	40	76.930408(8)	3.77(4) min	β^+	^77Kr	3/2−
^78Rb	37	41	77.928141(8)	17.66(8) min	β^+	^78Kr	0(+)
^78mRb	111.20(10) keV			5.74(5) min	β^+ (90%)	^78Kr	4(−)
					IT (10%)	^78Rb
^79Rb	37	42	78.923989(6)	22.9(5) min	β^+	^79Kr	5/2+
^80Rb	37	43	79.922519(7)	33.4(7) s	β^+	^80Kr	1+
^80mRb	494.4(5) keV			1.6(2) μs			6+
^81Rb	37	44	80.918996(6)	4.570(4) h	β^+	^81Kr	3/2−
^81mRb	86.31(7) keV			30.5(3) min	IT (97.6%)	^81Rb	9/2+
					β^+ (2.4%)	^81Kr
^82Rb	37	45	81.9182086(30)	1.273(2) min	β^+	^82Kr	1+
^82mRb	69.0(15) keV			6.472(5) h	β^+ (99.67%)	^82Kr	5−
					IT (.33%)	^82Rb
^83Rb	37	46	82.915110(6)	86.2(1) d	EC	^83Kr	5/2−
^83mRb	42.11(4) keV			7.8(7) ms	IT	^83Rb	9/2+
^84Rb	37	47	83.914385(3)	33.1(1) d	β^+ (96.2%)	^84Kr	2−
					β^− (3.8%)	^84Sr
^84mRb	463.62(9) keV			20.26(4) min	IT (>99.9%)	^84Rb	6−
					β^+ (<.1%)	^84Kr
^85Rb[n 10]	37	48	84.911789738(12)	Stable			5/2−	0.7217(2)
^86Rb	37	49	85.91116742(21)	18.642(18) d	β^− (99.9948%)	^86Sr	2−
					EC (.0052%)	^86Kr
^86mRb	556.05(18) keV			1.017(3) min	IT	^86Rb	6−
^87Rb[n 11][n 12][n 10]	37	50	86.909180527(13)	4.923(22)×10^10 y	β^−	^87Sr	3/2−	0.2783(2)
^88Rb	37	51	87.91131559(17)	17.773(11) min	β^−	^88Sr	2−
^89Rb	37	52	88.912278(6)	15.15(12) min	β^−	^89Sr	3/2−
^90Rb	37	53	89.914802(7)	158(5) s	β^−	^90Sr	0−
^90mRb	106.90(3) keV			258(4) s	β^− (97.4%)	^90Sr	3−
					IT (2.6%)	^90 Rb
^91Rb	37	54	90.916537(9)	58.4(4) s	β^−	^91Sr	3/2(−)
^92Rb	37	55	91.919729(7)	4.492(20) s	β^− (99.98%)	^92Sr	0−
					β^−, n (.0107%)	^91Sr
^93Rb	37	56	92.922042(8)	5.84(2) s	β^− (98.65%)	^93Sr	5/2−
					β^−, n (1.35%)	^92Sr
^93mRb	253.38(3) keV			57(15) μs			(3/2−,5/2−)
^94Rb	37	57	93.926405(9)	2.702(5) s	β^− (89.99%)	^94Sr	3(−)
					β^−, n (10.01%)	^93Sr
^95Rb	37	58	94.929303(23)	377.5(8) ms	β^− (91.27%)	^95Sr	5/2−
					β^−, n (8.73%)	^94Sr
^96Rb	37	59	95.93427(3)	202.8(33) ms	β^− (86.6%)	^96Sr	2+
					β^−, n (13.4%)	^95Sr
^96mRb	0(200)# keV			200# ms [>1 ms]	β^−	^96Sr	1(−#)
					IT	^96Rb
					β^−, n	^95Sr
^97Rb	37	60	96.93735(3)	169.9(7) ms	β^− (74.3%)	^97Sr	3/2+
					β^−, n (25.7%)	^96Sr
^98Rb	37	61	97.94179(5)	114(5) ms	β^−(86.14%)	^98Sr	(0,1)(−#)
					β^−, n (13.8%)	^97Sr
					β^−, 2n (.051%)	^96Sr
^98mRb	290(130) keV			96(3) ms	β^−	^97Sr	(3,4)(+#)
^99Rb	37	62	98.94538(13)	50.3(7) ms	β^− (84.1%)	^99Sr	(5/2+)
					β^−, n (15.9%)	^98Sr
^100Rb	37	63	99.94987(32)#	51(8) ms	β^− (94.25%)	^100Sr	(3+)
					β^−, n (5.6%)	^99Sr
					β^−, 2n (.15%)	^98Sr
^101Rb	37	64	100.95320(18)	32(5) ms	β^− (69%)	^101Sr	(3/2+)#
					β^−, n (31%)	^100Sr
^102Rb	37	65	101.95887(54)#	37(5) ms	β^− (82%)	^102Sr
					β^−, n (18%)	^101Sr

1. ^mRb – Excited nuclear isomer.
2. ( ) – Uncertainty (1σ) is given in concise form in parentheses after the corresponding last digits.
3. # – Atomic mass marked #: value and uncertainty derived not from purely experimental data, but at least partly from trends from the Mass Surface (TMS).
4. Bold half-life – nearly stable, half-life longer than age of universe.
5. # – Values marked # are not purely derived from experimental data, but at least partly from trends of neighboring nuclides (TNN).
6. Modes of decay:

   EC:	Electron capture
   IT:	Isomeric transition
   n:	Neutron emission
   p:	Proton emission

7. Bold italics symbol as daughter – Daughter product is nearly stable.
8. Bold symbol as daughter – Daughter product is stable.
9. ( ) spin value – Indicates spin with weak assignment arguments.
10. Fission product
11. Primordial radionuclide
12. Used in rubidium–strontium dating

Rubidium-87

Rubidium-87 is an isotope of rubidium. Rubidium-87 was the first and the most popular atom for making Bose–Einstein condensates in dilute atomic gases. Even though rubidium-85 is more abundant, rubidium-87 has a positive scattering length, which means it is mutually repulsive, at low temperatures. This prevents a collapse of all but the smallest condensates. It is also easy to evaporatively cool, with a consistent strong mutual scattering. There is also a strong supply of cheap uncoated diode lasers typically used in CD writers, which can operate at the correct wavelength.

Rubidium-87 has an atomic mass of 86.9091835 u, and a binding energy of 757,853 keV. Its atomic percent abundance is 27.835%, and has a half-life of 4.92×10¹⁰ years.

References

1. Meija, Juris; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265–91. doi:10.1515/pac-2015-0305.

• Isotope masses from:
  • Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
• Isotopic compositions and standard atomic masses from:
  • de Laeter, John Robert; Böhlke, John Karl; De Bièvre, Paul; Hidaka, Hiroshi; Peiser, H. Steffen; Rosman, Kevin J. R.; Taylor, Philip D. P. (2003). "Atomic weights of the elements. Review 2000 (IUPAC Technical Report)". Pure and Applied Chemistry. 75 (6): 683–800. doi:10.1351/pac200375060683.
  • Wieser, Michael E. (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)". Pure and Applied Chemistry. 78 (11): 2051–2066. doi:10.1351/pac200678112051. Lay summary.
• Half-life, spin, and isomer data selected from the following sources.
  • Audi, Georges; Bersillon, Olivier; Blachot, Jean; Wapstra, Aaldert Hendrik (2003), "The NUBASE evaluation of nuclear and decay properties", Nuclear Physics A, 729: 3–128, Bibcode:2003NuPhA.729....3A, doi:10.1016/j.nuclphysa.2003.11.001
  • National Nuclear Data Center. "NuDat 2.x database". Brookhaven National Laboratory.
  • Holden, Norman E. (2004). "11. Table of the Isotopes". In Lide, David R. (ed.). CRC Handbook of Chemistry and Physics (85th ed.). Boca Raton, Florida: CRC Press. ISBN 978-0-8493-0485-9.